This is to illustrate the volume difference between our 2 deep floors. One hive had the bottom planed off ( at Y) and so point X and point Y have different angles. Hive B required a greater volume of filling.
DF is Deep floor.

Here are some photos taken last summer ....

We could not find wire mesh anywhere so came up with this combination of plastic mesh (which we had already) reinforced with a board. The board is to deter Badgers.

Today we checked our bait hive, This one we forgot to put a nail across the entrance. It is over a door I go through every day and we hadn't seen any activity, although I do see a lot of birds in the garden gathering nesting materials. It is beautifully and deeply filled with fresh green moss, wool and horse hair. We put it straight back and will see what happens. Nesting would be finished in about 5 weeks if it gets used, about the right timing for a cast swarm at least. (temperatures still a little cool here but I''d say we are on the brink of our spring flow). I was delighted when I saw this though. imagining the bees finding the bait hive with a nature filled deep floor.
Kim

The bait hive in the previous picture was used as a birds nest, thankfully we didn't disrupt what had begun. As soon as the little ones fledged we took the hive down and put a nail across the entrance to prevent subsequent nesting.

We left the nesting material in to see if a swarm would choose it and it did receive a lot of interest but no swarm actually moved in. Being only my 2nd year I still had no brood comb to put in the hive to add to it's charm for a swarm. I did give it the odd drop of lemongrass. There are other bait hives within range of our bees. The swarm which looked very interested in the bait hive was still hanging in the tree after 4 or 5 hours so I chose for them by giving them a home.

I did then clean it out as I came by a piece of comb to put into it.

I still imagine that in the natural world many suitable bee cavities are previously used as nests and would be filled with nesting material.

I will try and get updated photos of our deep floors but until then, I have noticed that the deep floor now has a coating of propolis.

And .... the bees in one of the hives are using the gap that has appeared between the deep floor and the hive body as an entrance!

Conserving wild bees

Research suggests that bumble bee boxes have a very low success rate in actually attracting bees into them. We find that if you create an environment where first of all you can attract mice inside, such as a pile of stones, a drystone wall, paving slabs with intentionally made cavities underneath, this will increase the success rate.

Most bumble bee species need a dry space about the size a football, with a narrow entrance tunnel approximately 2cm in diameter and 20 cm long. Most species nest underground along the base of a linear feature such as a hedge or wall. Sites need to be sheltered and out of direct sunlight.